As biological tissue has relatively high permeability for long-wave light in the range of 700 to 1000 nm, a diagnostician can therefore use a completely different method of tissue imaging in addition to advanced medical imaging techniques such as X-raying, magnetic resonance tomography, or ultrasonic diagnosis.
Tissue-specific information can be obtained both by detecting the non-absorbed portion of radiation by means of a transmission image, and by detecting fluorescence radiation emitted after exposing the tissue to light in the near infrared range.
The main problem with the use of near infrared radiation is the extraordinarily wide scattering of light, which yields only a rather blurred image of a clearly contoured object despite different photophysical properties of such an object and its environment. This problem intensifies the greater the distance from the surface and may be considered the major limiting factor of both transillumination and the detection of fluorescence radiation.